Medical devices and instruments with non-coated superhydrophobic or superoleophobic surfaces

ABSTRACT

Device surfaces are rendered superhydrophobic and/or superoleophobic through microstructures and/or nanostructures that utilize the same base material(s) as the device itself without the need for coatings made from different materials or substances. A medical device includes a portion made from a base material having a surface adapted for contact with biological material, and wherein the surface is modified to become superhydrophobic, superoleophobic, or both, using only the base material, excluding non-material coatings. The surface may be modified using a subtractive process, an additive process, or a combination thereof. The product of the process may form part of an implantable device or a medical instrument, including a medical device or instrument associated with an intraocular procedure. The surface may be modified to include micrometer- or nanometer-sized pillars, posts, pits or cavitations; hierarchical structures having asperities; or posts/pillars with caps having dimensions greater than the diameters of the posts or pillars.

REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional PatentApplication Ser. No. 61/863,128, filed Aug. 7, 2013, the entire contentof which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to devices that come in contact withliquids, fluids, oils, gels, and the like and, in particular, to methodsand products of processes wherein at least a portion of such devices arerendered superhydrophobic and/or superoleophobic through microstructuresand/or nanostructures that utilize the same base material(s) as thedevice itself.

BACKGROUND OF THE INVENTION

The term hydrophobic/philic is often used to describe the contact of asolid surface with any liquid. The term “oleophobic/philic” is used withregard to wetting by oil and organic liquids. The term“amphiphobic/philic” is used for surfaces that are bothhydrophobic/philic and oleophobic/philic. Surfaces with high energy,formed by polar molecules, tend to be hydrophilic, whereas those withlow energy and built of non-polar molecules tend to be hydrophobic.

The primary parameter that characterizes wetting is the static contactangle, which is defined as the angle that a liquid makes with a solid.The contact angle depends on several factors, such as surface energy,surface roughness, and its cleanliness. If a liquid wets the surface(referred to as wetting liquid or hydrophilic surface), the value of thestatic contact angle is 0≦θ≦90 degrees, whereas if the liquid does notwet the surface (referred to as a non-wetting liquid or hydrophobicsurface), the value of the contact angle is 90 degrees <θ≦180 degrees.

Surfaces with a contact angle of less than 10 degrees are calledsuperhydrophilic, while surfaces with a contact angle between 150degrees and 180 degrees are considered superhydrophobic. It is knownthat surfaces exhibiting microscopic roughness tend to be hydrophobic.With such surfaces, air is trapped between the liquid and the substrate,causing the value of the contact angle to be greater than 90 degrees. Innature, water droplets on the surface of a lotus leaf readily sit on theapex of organic nanostructures because air bubbles fill in the valleysof the structure under the droplet. Therefore, these leaves exhibitconsiderable superhydrophobicity. The static contact angle of a lotusleaf is about 164 degrees.

One of the ways to increase the hydrophilic properties of a surface isto increase surface roughness. Studies showed that for micro-, nano- andhierarchical structures, the introduction of roughness increased thehydrophobicity of the surfaces. One such hierarchical structure,composed of a microstructure with a superimposed nanostructure ofhydrophobic waxes, led to superhydrophobicity with static contact anglesof 173 degrees. (See, for example: Bhushan, B., Jung, Y. C., and Koch,K., “Micro-, Nano- and Hierarchical Structures for Superhydrophobicity,Self-Cleaning and Low Adhesion,” Phil. Trans. R. Soc. A 367 (2009b)1631-1672, the entire content of which is incorporated herein byreference.)

Micro-, nano- and hierarchical patterned structures have been fabricatedusing soft lithography, photolithography, and techniques which involvethe replication of micropatterns, self assembly of hydrophobic alkanesand plant waxes, and a spray coating of carbon nanotubes. FIG. 1 is aschematic of a structure having an ideal hierarchical surface.Microasperities consist of the circular pillars with diameter D, heightH, and pitch P. Nanoasperities consist of pyramidal nanoasperities ofheight h and diameter d with rounded tops. In essence, with suchstructures, the nanostructures prevent liquids from filling the gapsbetween the pillars.

There are numerous applications for hydrophobic surfaces, includingself-cleaning, drag reduction, energy conservation and conversion. Ithas also been recognized that certain medical devices could benefit fromhydrophobic surfaces. Published U.S. Application No. 2013/0110222,entitled MEDICAL DEVICES INCLUDING SUPERHYDROPHOBIC OR SUPEROLEOPHOBICSURFACES, discusses the use of superhydrophobic/oleophopic surfaces fornumerous medical applications, but it is clear from this reference thatthe disclosure is limited to superhydrophobic/oleophopic coatings asopposed to engineered microstructures or nanostructures that use thesame base material as the device itself.

The preferred embodiments of the Published '222 Application prescribethe use of a slippery liquid-infused porous surface (SLIPS) comprising,for example, 1-butyl-3-methylimidazolium hexafluorophosphate. TheApplication states that “[s]tructured surfaces can also providecoatings, materials, or surfaces that are superhydrophobic,superoleophobic, or both. Suitable structure surfaces include thosedescribed in L. Mischchenko et al. ACS Nano 4 (12), 7699-7707 (2010),the disclosure of which is incorporated herein by reference. Suitablesilicon nanostructures can be fabricated according to the Bosch process(citations from Published Application omitted). These nanostructures arethen treated with a hydrophobic silane (e.g.,tridecafluoro-1,1,2,2-tetrahydrooctyl)-trichlorosilane) by vaporexposure in a desiccator under vacuum overnight.” ('222 Application;[0035]) “These structured surfaces can have geometrical features in theform of staggered bricks (e.g., subway brick pattern), posts, wideposts, blades, or honeycomb. Suitable geometrical features can bedescribed by pitch, height, and wall/post thickness ratio . . . ” ('222Application; [0036]).

SUMMARY OF THE INVENTION

This invention relates generally to devices that come in contact withliquids, fluids, oils, gels, and the like and, in particular, to methodsand products of processes wherein at least a portion of such devices arerendered superhydrophobic and/or superoleophobic through microstructuresand/or nanostructures that utilize the same base material(s) as thedevice itself.

A medical device according to the invention includes a portion made froma base material having a surface adapted for contact with biologicalmaterial, and wherein the surface is modified to becomesuperhydrophobic, superoleophobic, or both, using only the basematerial, excluding non-material coatings. The surface may be modifiedusing a subtractive process, an additive process, or a combinationthereof. The product of the process may form part of an implantabledevice or a medical instrument, including a medical device or instrumentadapted for use with an intraocular procedure.

In accordance with the invention, the surface adapted for contact withbiological material is modified to include micrometer- ornanometer-sized structures or patterns made from the base material. Forexample, the surface may be modified to include micrometer- ornanometer-sized pillars, posts, pits or cavitations; hierarchicalstructures having asperities; or posts/pillars with caps havingdimensions greater than the diameters of the posts or pillars.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a preferred structure having a hierarchicalsurface including asperities;

FIG. 2 is a diagram that shows potential fabrication techniques used tofabricate micron- and nano-scale structures;

FIG. 3A shows an array of pointed conical shapes applicable to theinvention;

FIG. 3B shows an array of tapered pillars with caps applicable to theinvention;

FIG. 3C shows an array of wider tapered pillars with caps applicable tothe invention;

FIG. 3D shows an array of shorter, tapered pillars applicable to theinvention;

FIG. 3E shows an array of short, coin-like structures;

FIG. 3F shows an array of narrower, tapered pillars with caps applicableto the invention;

FIG. 4A illustrates a woven superomniphobic surface;

FIG. 4B illustrates a random superomniphobic surface;

FIG. 5A shows a post or pillar having an inverse trapezoidalcross-section;

FIG. 5B shows a post or pillar having a non-inverted trapezoidalcross-section;

FIG. 5C depicts a preferred array of the structures of FIG. 5A;

FIG. 6 is an illustration that depicts intraocular scissors;

FIG. 7 is an illustration that shows a vitrectomy probe; and

FIG. 8 is an illustration that depicts intraocular forceps.

DETAILED DESCRIPTION OF THE INVENTION

This invention improves upon existing designs by providing medicaldevices with hydrophobic/oleophobic surfaces using the same material(s)that such devices are constructed from; that is, without resorting tocoatings. This is significant in that the substances used for suchcoatings may become detached during use and/or implantation, leading tocontamination, infection, and other undesirable side-effects.

FIG. 2 is a diagram that shows potential fabrication techniques used tofabricate micron- and nano-scale structures. In the preferredembodiments, reduction processes (i.e., lithographic and/or etching) arepreferred to additive steps such as deposition since the goal is toavoid material coatings. In the most preferred embodiments, e-beamlithographic and/or laser etching steps are used to create an array ofpillars on the surface being modified. The invention does not precludeadditive processes, however, so long as the same base material of thedevice is used to produce the additive microstructure. That is, if thebase material is metal (i.e., stainless steel, chrome-cobalt, etc.), ametallic microstructure or nanostructure is additively formed to achievea continuity in material type as opposed to dissimilar materials havinga greater tendency to separate and flake off. Thus, processes requiringsilicon (including the Bosch process), would not be recommended if asilicon coating is first required.

Different micro-/nanostructures are applicable to the inventiondepending upon the hydrophobic and/or oleophobic properties to beachieved in view of a given application. FIGS. 3A-3F show arrays ofshapes, certain of which may be more effective than other includingpointed conical shapes and tapered pillars with and without caps. FIG.4A illustrates a woven superomniphobic surface, and FIG. 4B illustratesa random superomniphobic surface.

Pillars formed in accordance with the invention may have straight sidesor may have tapered sides. Pillars with any cross-sectional shape may beused, including circular or polygonal with 3, 4, 5, 6 or more sides. Thepillars may have pointed or semi-pointed upper ends, as shown in FIGS.3A-3F. Preferably, the pillars have a diameter (D) in the range of 10microns or less, with a height (H) at least as tall as the pillars arewide. In more preferred embodiments, pillar height is 2-4 times thecross sectional height. Pillar spacing is preferably in the order of oneto three times D.

The structures of FIGS. 5A-5C are considered to be particularlyeffective. FIG. 5A shows a post or pillar having an inverse trapezoidalcross-section; FIG. 5B shows a post or pillar having a non-invertedtrapezoidal cross-section, and FIG. 5C depicts a preferred array of thestructures of FIG. 5A.

In certain preferred embodiments, the structure is hierarchical (FIG. 1)in the sense that one or more of the tops, sides, or spaces between thepillars includes asperities of height h in the range of 1 micron orless, depending upon the size of the pillars themselves. Preferably, theasperities are from 0.5 to .01 times the nominal thickness of thepillars, more preferably 0.1 times the nominal thickness. Suchasperities may be produced via chemical etching following pillarformation.

The above, coating-free hydrophobic/oleophobic surface modifications maybe used on any implantable on non-implantable medical device orinstrument. Substrates of metal, ceramics—even plastics—may be modifiedthrough appropriate engineering modification to the energeticbeams/etching modalities. The invention finds particular utility inproviding surgical instruments having hydrophobic/oleophobic surfaces,and more particular those used in intraocular procedures. Suchinstruments include, without limitation, intraocular scissors (FIG. 6);vitrectomy probes (FIG. 7); and intraocular forceps (FIG. 8). In theevent the instrument has one or more sharpened edges, such sharpeningmay be performed before or after the above surface modification, thoughsharpening following surface modification is preferred to produce thesharpest edge(s), while ensuring that any loose pillars are sloughed offprior to use.

1. A medical device, comprising: a portion made from a base materialhaving a surface adapted for contact with biological material; andwherein the surface is modified to become superhydrophobic,superoleophobic, or both, using only the base material, excludingnon-material coatings.
 2. The device of claim 1, wherein the portionforms part of an implantable device.
 3. The device of claim 1, whereinthe portion forms part of a medical instrument.
 4. The device of claim1, wherein the surface is adapted for contact with intraocular material.5. The device of claim 1, wherein the surface is modified to includemicrometer- or nanometer-sized structures or patterns made from the basematerial.
 6. The device of claim 1, wherein the surface is modified toinclude micrometer- or nanometer-sized pillars, posts, pits orcavitations using only the base material.
 7. The device of claim 1,wherein the surface is modified to include micrometer- ornanometer-sized hierarchical structures having asperities.
 8. The deviceof claim 1, wherein: the surface is modified to include micrometer- ornanometer-sized posts or pillars having diameters; and including uppercaps on the posts or pillars with dimensions greater than the diametersof the posts or pillars.
 9. The device of claim 1, wherein the surfaceis modified using a subtractive process.
 10. The device of claim 1,wherein the surface is modified using an additive process.
 11. Thedevice of claim 1, wherein the surface is modified using a combinationof additive and subtractive processes.
 12. A method of modifying amedical device having a surface adapted for contact with biologicalmaterial, comprising the steps of: modifying the surface to becomesuperhydrophobic, superoleophobic, or both, using only the base materialof the device itself, excluding non-material coatings.
 13. The method ofclaim 12, including the step of modifying the surface to includemicrometer- or nanometer-sized structures or patterns made from the basematerial.
 14. The method of claim 12, including the step of modifyingthe surface to include micrometer- or nanometer-sized pillars, posts,pits or cavitations using only the base material.
 15. The method ofclaim 12, including the step of modifying the surface to includemicrometer- or nanometer-sized hierarchical structures havingasperities.
 16. The method of claim 12, including the steps of:modifying the surface to include micrometer- or nanometer-sized posts orpillars having diameters; and forming upper caps on the posts or pillarswith dimensions greater than the diameters of the posts or pillars. 17.The method of claim 12, including the step of using a subtractiveprocess to modify the surface.
 18. The method of claim 12, including thestep of using a subtractive process to modify the surface.
 19. Themethod of claim 12, including the step of using a combination ofadditive and subtractive processes to modify the surface.
 20. A productmade using the process of claim 12.